Recent advances in digital and communications technology have enabled the relatively easy distribution of AudioVisual (AV) works, such as images, audio tracks and movies, in the form of digital data. The Internet is frequently used to distribute digital copies of such works and this in itself poses a serious problem in terms of maintaining copyright protection. As a result of this, techniques of electronic watermarking have received a great deal of attention as a way of detecting and combating illicit use of these AV works. Typically, these techniques involve embedding a digital watermark identifying the copyright owner, the provider, the user and/or even the permitted uses of the work, into the AV data in such a way as to make the watermark undetectable by the user. If the data is used in an unauthorised manner or by an unauthorised person, then by comparison of the watermark data with the known user data, this illicit use can be detected.
There are many different methods of generating digital watermarks which involve various time/frequency domain transformations, encryption techniques and other data manipulation techniques (see for example EP-A-0 953 938 and WO-A-99/17537). However, when transaction specific information is to be included in the watermark, these existing methods involve creating the digitally watermarked version of the AV work on demand. In practice, this process involves some form of data computation on the whole or most of the media file representing the AV work. The time taken to create such watermarked AV work is proportional to the size of the media file of the AV work and, due to the continual trend towards increasing file sizes, the creation time is also getting longer. This problem makes the above existing watermarking techniques unsuitable for transaction specific watermarking of AV works in real-time which can also cause difficulties with highly desirable facility of accessing AV works via the Internet.
The issues associated with real-time watermarking have been described fully in co-pending European Patent Application No. 99309133.9, which addresses the problem of applying watermarking in real-time to the digital data to be distributed.
Co-pending European Patent Application No. 99309133.9 describes a solution in which a transaction-specific watermark is applied to a subset of the complete media file, allowing a sample of the file to be obtained without the transaction-specific watermark having to be applied to the complete file. This is done in away that ensures that if multiple samples are obtained, their watermarks combine to provide a useable watermark on the collection of samples. However, this method still requires the watermarking to be applied in real-time to those parts of the complete file that are being transferred to a customer. The method succeeds in reducing the computation time required to provide samples of the media file for evaluation, but still does not address the problem of watermarking the complete file in real time when/if the final purchase is made.
Applying a digital watermark to a complete media data file requires substantial computation, and it is difficult to do this at realistic cost or at a speed that will not delay real-time interaction by electronic trading for example.
Accordingly it is desired to overcome or substantially reduce the above mentioned problems. More specifically, it is desired to provide a method of digitally watermarking a complete media file in real time to minimise the delay during a customer interaction for example.